1. Field of the Invention
The present invention relates to spherical beads of cross-linked glucomannan, in particular, those which are useful, for example, as packing material in the techniques of gel filtration and gel chromatography, and to a process for their production.
2. Description of the Prior Art
For isolation or fractionation of substances by making use of the difference in the molecular size, techniques have been developed in, for example, so-called gel filtration and gel chromatography. The gel filtration and gel chromatography employ as the packing material gelled particles of hydrophilic or hydrophobic nature and there have been in practical use, for example, beads of such materials as dextran, agarose, cellulose, polyvinyl alcohol, polyacrylamide and polystyrene.
Important properties for the packing material for gel filtration and gel chromatography are the stability against pressure in water, namely, the strength to maintain spherical shape of beads, and the capability of voluntary selection of the exclusion limit molecular weight, namely the upper permissible limit of molecular weight of solute to penetrate through the beads, among wide distribution range thereof. Such properties are important for isolating the objective substance in a form as pure as possible among those which have moleculr weights distributed over a wide range and for maintaining a uniform packing condition without suffering from destruction or deformation of the beads.
The conventional gel beads of hydrophobilic or hydrophobic nature found in practical use as mentioned above are not only difficult to obtain in the form of fine particles of true spherical shape, but also are inferior in the strength, besides the shortcoming that it is difficult to attain adjustment of the exclusion limit molecular weight over a wide range.
In the magazine "Nippon Kagakukaishi" No. 5, p. 732 (1984), there is a report for "Hydrophilic Gels from Mannan Grafted by Vinyl Acetate as Gel Chromatographic Packings". Here, it is reported that "graft copolymers, which contain 54, 71 and 84 mole % of pendant poly(vinyl acetate) and whose degree of polymerisation was about 2,000, were synthesized by grafting vinyl acetate to mannan granules which contained an aqueous solution of potassium peroxodisulfate. Beads of acetylated graft copolymer were prepared by suspending a solution of acetylated graft copolymer in dichloromethane in an aqueous medium. Then, beads of mannan-poly(vinyl alcohol) graft copolymer were prepared from the beads of acetylated graft copolymer by saponification and subsequent cross linking". In the hydrophobic gel obtained herein however, "highly hydrophilic micro mannan gel phases exist in the poly-(vinyl alcohol) gel matrix". Thus, they are not quite excellent for the packing material for gel filtration etc.
There were reported in the magazine "Polymer Preprints, Japan", Vol. 36, No. 3, 876 (1987). .circle.1 that glucomannan beads suitable for aq. base GPC were prepared by forming micro beads of triacetyl glucomannan by suspension evaporation, saponifying them in heterogeneous phase and cross-linking them with epichlorohydrin, .circle.2 that glucomannan beads having exclusion limit molecular weights in the range of 10.sup.2 -10.sup.7 or more were able to be obtained by regulating the condition of the cross-linking reaction and selecting the diluent and its concentration during the formation of beads and .circle.3 that this gel exhibited quite lower swellability than conventional hydrophilic gel.
In this report, however, the method of preparation of gel is given only conceptionally and it is not guaranteed that a superior gel product is always obtained. The material properties of the gel are not clear.